AWS Sign provides classes for signing AWS HTTP requests adhering to the signature version 4 specification.
Additionally, a tornado based HTTP client capable of sending signature v4 signed requests is provided.
Request signing requires many inputs, one of which is a set of values representing the AWS service : this includes, but not limited:
- host
- service name
- region
- signing algorithm
ServiceConstants provides a logical grouping of these values.
Services that require more constants can subclass ServiceConstants and inherent default behaviors. As an example, consider a class representing APIGateway. ServiceConstants doesn't sufficiently represent all the constants needed to sign requests so we must create a sublcass.
class APIGatewayServiceConstants(Sigv4ServiceConstants):
# Parsed by 'from_url' method. Matched group array is passed as *args list to
# constructor so ordinal positions of match values must match constructor args.
URL_REGEX = re.compile(r"""(?:https://)? # scheme
(\w+ # api prefix
\.
([\w\-]+) # service
\.
([\w\-]+) # region
.amazonaws.com)
\/
([\w]+)$ # stage""", re.X)
def __init__(self, *args):
"""
Parameters
host: service host
service: service name
region: service region
stage: api gateway stage
"""
super(APIGatewayServiceConstants, self).__init__(*args[:3])
self.stage = args[3]
@property
def url(self):
return 'https://%s/%s' % (self.host, self.stage)
def __str__(self):
return 'host=%s\nservice=%s\nregion=%s\nstage=%s\nalgorithm=%s\nsigning=%s\nheaders=%s' % \
(self.host, self.service, self.region, self.stage, self.algorithm, self.signing, self.headers)Consider another example using dynamodb
class DynamoDBServiceConstants(Sigv4ServiceConstants):
__REQUIRED_HEADERS = {'content-type':None, 'x-amz-target': None}
def __init__(self, *args):
super(DynamoDBServiceConstants, self).__init__(*args)
self.__headers = self._merge(super(DynamoDBServiceConstants, self).headers,
self.__REQUIRED_HEADERS)
@property
def headers(self):
return self.__headersNote that DynamoDBServiceConstants has inherited host and x-amz-date headers from Sigv4ServiceConstants instance.
>>> sc = DynamoDBServiceConstants.from_url('https://dynamodb.us-west-2.amazonaws.com')
>>> pprint.pprint(sc.headers)
{'content-type': None,
'host': 'dynamodb.us-west-2.amazonaws.com',
'x-amz-date': None,
'x-amz-target': None}auth.Authorization encapsulates the signing behavior. Invoke the header instance method to get the
HTTP 'Authorization' header data necessary for signed requests. Also note that signing values can be encoded
in querystring parameters.
...
a = auth.Authorization(ServiceConstants(*args), Credentials())
# Sign request
http_headers['Authorization'] = a.header(**kwargs)
...TBD
AWS Sign is free software and is released under the terms of the MIT license (http://opensource.org/licenses/mit-license.php), as specified in the accompanying LICENSE.txt file.
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